Ignition timing



Aug. 7, 1945. H, T. JARws 2,380,967

IGNITION TIMING Filed March 5o, 1943 2 sheets-Sheet 1 Aug. 7, 1945. H.T. JARvls IGNITION TIMING Filed Marc-:h 30, 1943 2 Sheets-Sheet l Eg.

All? HE TFH/ I SECT/0N l CAHHURETM INVENTOR Harold Jarvls am f M50Ar'roRN'gY.

Patented Aug. 7, 1945 UNITED STATES PAT-ENT opsteli 2,380,967' JGNrrroNTIMJNG HaroldvT. Jarvis. Manchester; Conn., assigner to -United AircraftCorporation, East Hartford,

Conn., a corporation of Delaware 'Application Marenso, 1943, serial No.481,114`

comme (c1. 12s- 117) concentric with restriction 34. A diaphragm 38 Thisinvention relates to improvements in intemal combustion engines, withparticular reference to improved ignition timing control.

An object of the invention is to provideanA automatic control includinga servo-motor for changing the ignition timing, a device operating theservo-motorcontrol and means operative in response to variations in therate of intake mass air ow operating the control device.

A further Objectis toprovi'de a control apparatus in which the controlis eiected by a device is mounted in a chamber 40 adjacent the venturisand the space at one side of the diaphragm is connected with the airpassage on the upstreamA side. of the 4Venturi restriction throughchannels 42 and 45, the temperature and pressure compensating valve 48and the ram tubes 50 while the space at the opposite side of diaphragm3Q is accurately responsive to variations in the rate oi f intake massair ow through the carburetor and in which the relatively large pressurerise across the engine supercharger is used as the motivating force.

Other objects and advantages will be apparent from the speciiication andclaims, and from the accompanying drawings which illustrate what is nowbelieved to be a preferred embodiment of the invention.

In the drawings, Fig. 1 is a schematic view of an ignition timingcontrolapparatus constructed according to the invention.

Fig. 2 is a sectional view of one of the magneto' drive units taken onthe line 2 2 of Fig. 1.

Fig.'3 is a view online 3-3 oi Flg.2.

Fig. 4 is a diagrammatic view of a portion of the apparatusl shown inFig. 1 showing a somewhat modied form oi control apparatus.

Referring to the drawings a supercharged, electric ignition,internal-combustion engine l0 having a plurality of cylinders, one ofwhich isindicated at I2, is provided with ignition apparatus which mayinclude a pair of magnetos I4 and i6l driven by the engine andelectrically connected with the engine spark plugs as indicated at I1, a

with an intake supercharger generally indicated at i8 and with acarburetor, a portion or which is shown in Fig. 1 andgene'rallyindicated at 20.

The superchargerhas an outerdiiiuser casing 22 connected with the enginecylinders through a pipe 24, an air intake 25, andan impeller 28 on anenginedriven shaft 28.'v When-the Aengine is operatingthe pressure risebetween intake 25 and' discharge casing 22` will increase with the speedoftheimpeller. y f'- All air entering the engine passes through in-v'take passage Il! of the carburetor, which is conventionally located inthe induction passage 25 leading to the supercharger I8. Within thispassage is a throttle valve 32 and a Venturi restriction 34. In' orderto render venturi -34 sensitive toextremely low rates of intake air ilowAan auxand 88 oi' the `and lll.' iliary venturi. may be installedsubstanti-ally 55 As the two gear trains are similar in all reconnectedwith the interior of the throat ofthe auxiliary restriction 36 throughthe channel 52. With this arrangement, air flowing through intakepassage 30 creates a pressure differential across diaphragm 38 andimposes on .the stem 54- a force which is a measure of the ra' oi intakeairow.

The air imposed force on stem1 54 is balanced against a fuel imposedforce by additional apparatus not shown in Fig. l'but illustrated inFig. 4, wherein a chamber 58 contains adiaphra'gm 58v which is alsoconnected at its center to the stem 54. Stem 54 extends beyond diaphragmBand carries a valve 60 which cooperates with a vvalve seat formed in awall 62 interposed between the chamber 56 and a chamber 84 into whichfuel is pumped by a pump 86. Fuel 'may ilow from chamber 84 past valve60 into the space in-cliamber I6 on the valve side oi.' diaphragm 5B andfroml this space through channel 68, apertures 10' and 12 and conduit 14to the conventional discharge valve or injection nozzle, notillustrated. The

space on the `side of the diaphragm 58 opposite valve 60 is connectedthrough channel 16 with apertures 10 and 12. Aperture 10 is* controlledby a fuel mixture control valve 18 and aperture 12 is l controlled by aneconomizer valve 8U. With this f arrangement, fuel n owing from pump toconduit 14 exerts a pressure on diaphragm B8 opthe quantity of air andthe quantity of -fuel in the mixture supplied/to the engine.

Magnetos i4 and IB are drivenirom the engineby means schematicallyillustrated in Fig. 1 and comprising an engine driven shaft 82, 'gears86,

shaft 84 and vadilistwble gearltrains indicated at .88 and 90. Shaft hasat its ends bevel gears 2 and 94 which meshrespectively with gears 96two magneto drive'gear trains 88 posed t o the pressure exerted ondiaphragm i8' by' spects, a description of only one of them will besuflicient for the present purpose. Gear 86 is rigidly secured to anoppositely beveled gear 88 (Fig. 2) supported for free rotation on theouter end of magneto drive shaft |00. Gear 98 meshes with a pair ofidler gears |04, |06 carried by a cage |08 supported onshaft |00, whichis freely rotatable therein. Idler gears |04 and |06 mesh with a drivegear xed on |00 by pin ||2. The drive is therefore from shaft 84 throughgears 82 and 86 to gear 98 and thence through idler gears I 04 and |06to gear |0. With this arrangement, it is apparent that rotation of cage|08 about shaft |00 will angularly displace gear ||0 relative to gear88, resulting in an angular displacement of shaft |00 relative to enginedriven shaft82, and a consequent change in the timing of the magnetdriven by shaft |00. f

Rotational movement of the cages of both magneto drive, about themagneto drive shafts, is controlled by a servo device |0| comprising adouble ended piston |24 slidable in axially aligned cylinders |26 and|28 and connected with the cages of the magneto gear trains by a yoke|30 and a cross bar |32 pivotally connected at its ends to two arms |34and |36 extending radially from the idler gear cage |08 of gear trains88 and 90 so that movement of piston |24 will effect a change inthetiming of the magnetos.

Within cylinder |28 is a compression spring |38 which urges piston |24towards its spark retarding position against the end of a stop |40 incylinder |26 .and telescopically associated with hollow piston |24. Asimilar stop |42 in cylinder |28 limits the movement of the piston inthe spark advancing direction. Stops |40 and |42 are integral with thescrew plugs which close the ends of cylinders |26 and |28.

Operation of the servo motor |0| is controlled by the hydraulic valve|44. This valve comprises a hollow casing |46 having at one side thereofspaced ports connected with a pressure line |52 and a pair of drainlines |54 and |56 disposed one at each side of the pressure line |52.The pressure line may be connected with some suitable source ofhydraulic uid under pressure such as the engine lubricating oil pump,not illustrated. The opposite side of the valve casing is provided withspaced valve ports from which fluid conduits |58 and |60 lead to theopposite ends of servo motor 0|. As illustrated, conduit |58 leads tothe interior of the cylinder |26 adjacent the closed end thereof and theconduit |60 leads to the interior of the cylinder |28 adjacent the'closed end thereof. Within the hollow valve casing |46 there is areciprocable plunger |62 having a pair of reduced portions terminated byspaced piston portions |64, |66 and |68. From the above description,taken in connection with the accompanying drawings, it is apparent thatwhen the plunger |62 occupies its uppermost position, as illustrated inFig. 1, the conduit |58 is connected with `the drain channel |54 and theconduit |60 is connected with the pressure channel |52 thus applyingpressure to the right hand end of the piston of the servo motor andmoving this piston to its limiting left hand position, as

illustrated, thereby retaining the magneto adjustment at a retardedspark position. When plunger |62 occupies its lowermost position, theconduit |58 is connected with the pressure channel |52 thus applyingpressure to theleft hand side of the piston |24 of the servo motor andmoving this pisjton toits limiting right hand position to advance themagneto spark setting.

At the upper end of valve casing |46 there is a chamber |10 transverselydivided by a flexible diaphragm 12 connected at its center to the end ofvalve plunger |48. The space at the upper side of diaphragm |12 isconnected through conduit |14 with the diffuser portion 22 of thesupercharger and the space below diaphragm |12 is connected throughconduit |16 with the supercharger inlet 25. With this arrangement thepressure rise across the supercharger from the inlet to the outlet willtend to force the diaphragm downwardly and move valve plunger |64 to aposition in which it actuates the servo motor |0| to advance the sparksetting. The diaphragm is continuously urged toward its upper position,as illustrated, by a calibrated compression spring |18 which iseffective to maintain the diaphragm in its upper, spark retarding,position until the pressure rise across the supercharger has reached acertain predetermined value.

A casing |80is provided adjacent the carburetor and within this casingare two chambers |82 and |84. Within the chamber |84 is 9. transversediaphragm |86 connected at its center to a stem |88 which projectsthrough the chamber |82 and carriesat its end a valve |80 cooperatingwith a valve seat provided in the outer wall of chamber |82.. A conduit|82 leads from the conduit |16 to the chamber 82 and a conduit |84 leadsfrom the conduit |14 to a pocket |86 provided in the chamber andseparated from the chamber |82 by valve |80. With this arrangement, whenthe valve |80 is opened, the conduits 82 and |84 and consequently theconduits |14 and |16, will be connected through this valve and thepressure differential across the diaphragm |12 will be bled away. Inorder to facilitate this bleeding operating the conduits |14 and 16 areprovided with restricted orifices |88 and 200 each vhaving a crosssectional area less than the free passage through the valve |80.

In the form of the invention shown in Fig. 1, the space within thechamber |84 at the left hand side of the diaphragm |86 is connected by achannel 202 with the interior of the intake air passage 30 and the spaceat the right hand side of this diaphragm is connected through a channel204 with the channel 52 leading from the throat of the venturi 36. Withthis arrangement the Venturi pressure drop will impose a force ondiaphragm 12 tending to open valve |80. A calibrated compression spring206 opposes the force f right hand side of the diaphragm' |86 isconnected through a conduit 2|0 with the space at the left hand side ofthe fuel iiow responsive diaphragrn 58. 'With this arrangement, thepressure exerted by the fuel in flowing to the'conduit 14 is exerted onthe diaphragm |86 in adirection to open the valve |80. 'Ihe operation ofthe diaphragm |86 is exactly the same asthat described above inconnection with Fig. 1 except that in Fig. 4 the fuel pressure isutilized to open the lvalve |80 as it has been found that the use of theliquid fuel for this purpose embodies certain advantages, particularlyin that the liquid fuel is not compressible and therefore prevents anytendency of the valve |90 to chatter.

Operation 4threeinches of mercury on a manometer reading has beenselected for certain installations, and for the upper limit of thecruising range a carburetor metering pressure indicated by a manometerreading of 17 inches of Water has been selected. With the abovedescribed app-aratus,

the compression spring |18 may be calibrated for the starting and idlingrange so that it will not permit the diaphragm |12 to move until thelimiting value of this range is reached. As the supercharger impellerhas a relatively slow rate of rotation in the starting and idling rangeof engine operation it will not exert a supercharger `rise pressuredifferential exceeding that for which the spring |18 is calibrated andtherefore spring HS alone may be depended upon to maintain a retardedspark setting for the starting and idling operation. When the enginespeed reaches a value at which the pressure rise across the superchargerexceeds the force of the spring |18 the diaphragm |12 will be moveddownwardly thus actuating the servo motor IUI to advance the sparksetting of the engine. The diaphragm |86, however, does not respond atthese operating conditions and the valve |90 remains closed. If

. the engine speed and power increased to a value at which the meteringpressure exceeds the upper limit of the cruising range, for exampleseventeen inches of water manometer reading, the diaphragm |86 will bemoved to open the valve |90. Opening this valve Will interpose a bleedacross the conduits |14 and .|16 permitting the diaphragm |12 to riseunder the force ofA the spring |18 thus moving the plunger |62 to aposition at which the servo motor Illl is actuated to again retard theignition timing for the high power engine operation.

i It is to be understood that the invention is not limited to thespecific embodiment herein ilustrated and described, but may be used inother ways without departure from its spirit as defined by the followingclaims.

I claim:

1. In combination with an engine having an adjustable ignitionapparatus, an intake air supercharger, and an carburetor having meansfor establishing a uid pressure head `proportional to the rate of flowof engine intake air, a servo-motor for adjusting said ignitionapparatus, means operated by the pressure rise across said superchargercontrolling said servo-motor, and means operated by said carburetorpressure head controlling said servo-motor control means.

2. In combination with anengine having an adjustable ignition apparatus,an intake air supercharger, anda carburetor having means forestablishing a fluid pressure head proportional to the rate of flow ofengine intake air, a servomotor for adjusting said ignition apparatus, avalve operated by the pressure rise across said supercharger controllingsaid servo-motor, and a device operated by said carburetor pressure headwhich renders said supercharger pressure rise in- 4 effective to operatesaid valve when said carburetor pressure head exceeds a predeterminedvalue.

3. In combination with an engine having an .adjustable ignitionapparatus, an intake air supercharger, and a carburetor having means forestablishing a fluid pressure head proportional to the rate'of flow ofengine intake air, a servo-motor for adjusting said ignition apparatus,means operated by the pressure rise across said supercharger controllingsaid servo-motor, and means operated by said carburetor pressure headcontrolling said servo-motor control means, a valve controlling saidservo-motor, a spring urging said valve in an ignition retardingdirection, means operated by the pressure rise across said superchargerto move said valve to an ignition advancing position when said pressurerise exceeds a predetermined value, and means operated by Saidcarburetor pressure head to render said pressure rise operated meansineffective to retain said valve in an ignition advancing position whensaid carburetor pressure head exceeds a predetermined Value.

4. In combination with an engine having an adjustable ignitionapparatus, an intake air supercharger, and a carburetor having means forestablishing a fluid pressure head proportional to the rate of flow ofengine intake air, a servomotor for .adjusting said ignition apparatus,means operated by the pressure rise across said supercharger controllingsaid servo-motor, and means operated by said carburetor pressure headcontrolling said servo-motor control means, a Valve controlling saidservo-motor, a spring urging said vvalve in an ignition retardingdirection, means operated by the pressure rise across said superchargerto move said valve to an ignition advancing position when said pressurerise exceeds a .predetermined value, a valve operative when open torender said pressure rise operated means ineffective to retain saidvalve in an ignition advancing position, means actuated by saidcarburetor pressure head to open said valve, and a spring opposing thevalve opening tendency of said pressure head operated means andmaintaining said valve closed until said pressure head exceeds apredetermined value.

5. In a device for changing the timing of an engine ignition system, aservo-motor operated by fluid pressure from a iirst source for moving atime controlling element of said ignition system, a first valve movableby fluid pressure from a second source to reverse said servo-motor bychanging the fluid connections between said servo-motor and said firstsource, and a second valve movable by a third source of fluid pressureto modify the effect of pressure from said second source on said firstvalve when the pressure from said third source exceeds a predeterminedvalue.

6. In an aircraft engine having an adjustable ignition system, mechanismfor adjusting the timing of said ignition system, means for actuatingsaid mechanism in accordance with changes in an engine operatingcondition, measuring means for establishing a uid pressure differentialwhich is a measure of the mass rate of ow of intake air to said engine,and means responsive to variations in said fluid pressure differentialfor modi- I fying the actuation of said mechanism by said actuatingmeans.

HAROLD T, JARVIS.

